Is there a way to do this inside Memgraph with triggers?

Question

When calling a query module from a trigger statement, what I expected to get within a function was a state of the graph before the query changes occurred. However, this is not the case, and made changes are already visible in the graph state. I’ll write a dummy example of such behavior:

CREATE TRIGGER my_trigger ON CREATE
BEFORE COMMIT EXECUTE
CALL my_module.function(createdVertices, createdEdges) YIELD node, property
SET node.property = property;

Function my_module.function should execute after following statement:

MATCH (n {id: 19}), (m {id: 10}), (u {id: 14})
CREATE (n)-[new_edge_1:RELATION]->(m), (n)-[new_edge_2:RELATION]->(u)

In my_module.function, we’ll see a graph state with just created new_edge_1 and new_edge_2. If our calculation depends on having incremental changes, where we need the state of graph before any changes occur, is there a way to do it inside Memgraph with triggers?

score 0 · Accepted Answer · answered Oct 24 '22 at 07:12

Unfortunately, there is no way to do that with the triggers. During a single transaction, the changes of each query are visible in the next query. Triggers basically execute their statements as a query that is part of that transaction (if the BEFORE COMMIT is used). You could probably use the changed values and ignore edges that are created in that transaction.

Is there a way to do this inside Memgraph with triggers?

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